On March 20, 2003 the United States headed a coalition with the UK and other forces to invade Iraq.

On March 20, 2003 the United States headed a coalition with the UK and other forces to invade Iraq. (Chris Hondros / Getty Images)

Ten years have passed since the United States invaded Iraq, a decision that almost everyone now ranks as one of the worst foreign policy blunders of our time. Why "almost"? Former President George W. Bush and his top aides still maintain that the invasion was a good idea, even though the premise on which the war was based — that Saddam Hussein had acquired weapons of mass destruction — proved false, and even though the ensuing war claimed the lives of more than 4,500 Americans and an estimated 127,000 Iraqis.

The debate over what went wrong — which is also a debate over who deserves blame — is still under way. Was it bad intelligence? Bad policymaking? A spineless Congress? Insufficiently skeptical media? Or, most likely, all of the above?

But the more important question for the future is this: Have we learned enough from the experience to make a difference the next time? It would be nice if the question were hypothetical, but it's not. The U.S. conflict with Iran is different from the confrontation with Iraq in many ways, but it's the same intelligence services gathering information and the same political system that will make the calls.

At the risk of simplifying a rich and tangled history of failure, three big things went wrong in the Bush administration's decision to go to war with Iraq. The first was hubris: the belief that a U.S. invasion could not only topple Hussein quickly (as it did), but also produce a swift, low-cost transition to democracy (which it didn't). The second failing was flawed intelligence: the assumption, abetted by bad information, that because Hussein had been working on weapons of mass destruction before, he must have been doing it still. The third was misuse of intelligence: the relentless hyping of the case against Hussein by the advocates of war, who took ambiguous information and warned, in the words of then-Secretary of State Condoleezza Rice, that "We don't want the smoking gun to be a mushroom cloud."

Let's take the three in turn.

When it comes to hubris, we've been cured — at least for a while. There's nothing like a decade of grinding war to teach that invasions aren't easy and counterinsurgency isn't short. If anything, the Obama administration has overlearned the lesson, hesitating long and hard before backing even indirect military aid to insurgents in Syria.

But no lesson lasts forever. It took only 15 years after the traumatic end of the Vietnam War for the United States to launch another large-scale military expedition, the 1991 Gulf War against Iraq.

When it comes to intelligence, the CIA and other agencies have made earnest efforts to ensure that they don't make the same mistakes again. For many analysts, the Iraq episode was a crushing professional failure. "You cannot make excuses for the intelligence," John E. McLaughlin, the CIA's second-in-command at the time, told me last week. "It's constantly in the forefront of your mind.... It's been a decade of real introspection."

Since Iraq, the CIA and other agencies require that top officials personally guarantee the quality of the intelligence they deliver. They're more explicit about the reliability (or unreliability) of their sources. And they subject major judgments to "red teams," adversarial exercises to see if other findings are reasonable.

So can an intelligence failure happen again? "Of course it can," McLaughlin said. "You're dealing with incomplete information, arriving incrementally, under pressure to come to definitive conclusions … and much of the information is laced with deception. You can't ever guarantee that there won't be a mistake."

The third problem is the most difficult: the politicization of intelligence information. In the run-up to the invasion, top Bush administration officials repeatedly exaggerated the case against Hussein in a determined campaign to convince Congress and the public that war was necessary.

Chief among the exaggerators was Vice President Dick Cheney, who told the public that the United States was certain that Hussein had "reconstituted" his chemical, biological and nuclear weapons programs, and that one of the Sept. 11 hijackers had met with an Iraqi intelligence official, a claim that was later debunked.

Intelligence officers knew that at least some of that information was wrong, but they hesitated to dissent from their superiors — and those who did had no easy way to correct the public record.

Even when intelligence officials went public with misgivings, it didn't always matter. At one point, McLaughlin told the Senate Intelligence Committee that the CIA didn't think Hussein was likely to use chemical weapons against the United States. "It made no discernible impact" on the debate, he said.

Some intelligence veterans don't think this problem has been solved at all.

"Most of the lessons have not been learned," said Paul R. Pillar, who was one of the CIA's chief Middle East analysts in the lead-up to the war. He contends that even if the intelligence community had reported accurately that Hussein had no weapons of mass destruction, the Bush administration would still have won congressional approval for a war.

Pillar has proposed making the CIA an independent agency like the Federal Reserve, with a 10-year term for its director to insulate him from political pressure. But he doesn't expect that to happen soon.

So have we learned enough to prevent another ill-advised military adventure?

In the short run, at least, we're not likely to blunder into another land war — in Iran or anywhere else. Intelligence judgments are likely to get more scrutiny from Congress, the media and the public. Intelligence officers will be less hesitant to blow the whistle, too.

But will those lessons be remembered 15 or 20 years from now? If history is a guide, don't count on it.

In 2011, the U.S. ambassador to Syria, a mild-mannered diplomat named Robert S. Ford, became the face of American support for the Arab Spring when he boldly visited opponents to the brutal regime of Bashar Assad in the northern city of Hama.

After 13 years of war, more than 2,300 dead U.S. troops and the replacement of the Taliban regime with an elected government, the United States this past weekend declared a formal end to its combat mission in Afghanistan. That's an important symbolic marker, but no one should interpret the declaration...

Imagine President Franklin Roosevelt announcing at the end of 1944, after the liberation of France but before the final defeat of Nazi Germany and Imperial Japan, that World War II was over and that U.S. forces were ending combat operations. Instead we would support our allies, from Britain to...

President Obama's announcement Wednesday that the U.S. would resume diplomatic relations with Cuba after more than a half-century is, indeed, a historic event. It's also something of an afterthought to the Cold War, which has been history itself for more than two decades now.

At the dawn of 2015, the U.S. has yet to articulate a comprehensive foreign-policy strategy to counter the influence and territorial gains of Islamic State, the terrorist group that emerged last year — and poses a dangerous and vexing threat to stability across the Middle East and North Africa....

The Senate Intelligence Committee's "torture report" has reignited national debate on "enhanced" interrogation techniques. At the heart of this debate is the question: Do these methods work to prevent terrorist attacks?

The United States has the most potent military in terms of firepower and operational capacity in history. Our military overthrew Saddam Hussein and crushed the Taliban in a matter of weeks. Our forces can direct a rocket from Nevada through a window in Kandahar, Afghanistan, and nimbly set up nearly...